Compressor mechanism



Patented Mar. 9, 1948 COMPRESSOR MECHANISM Burton S. Aikman, Wilkinsburg, Pa., assignor to The Westinghouse Air Brake Company, Wilmerding, Pa., a corporation of Pennsylvania Application January 29, 1944, Serial No. 520,288

This invention relates to steam driven fluid compressors and more particularly to the type employed on locomotives in steam railway service.

The ob'ect of my invention is to provide a steam driven compressor having novel means for effecting an economy in steam consumption by utilizing the exhaust steam to effect a supply of supercharging air to the compressor and thus obtain the delivery of air at higher pressures with the same supply of steam.

Other objects and advantages will be apparent from the following more detailed description of the invention.

In the accompanying drawing the single figure is a diagrammatic vertical sectional view of a cross compound steam driven air compress-or having the invention embodied therein.

Referring to this drawing, the compressor comprises a steam actuated driving portion, designated by the numeral I, which is covered by a valve portion 2, and to the bottom of which is secured by suitable means; not shown, an intermediate connecting portion 3. Mounted on the bottom of the portion 3, is an air compressing portion 4 which is closed at-the bottom by a cover portion 5. Disposed at the left-hand side of the several aforementioned portions is a supercharger portion 6 which ma; be formed integral with the steam portion I and which is closed at the top by a cover portion 1.

Contained in the cylinder 8 of the steam portion I is a high pressure steam piston 9. which is connected by a rod IE! to a high pressure air piston I I carried in the cylinder l 2 of the air compressing portion 4. Similarly, a low pressure steam piston I3 is contained in the cylinder M of the steam ortion I and is connected by a rod [5 to the low pressure air piston l6 disposed in the cylinder I! of the portion 4.

The supercharger portion 6 is provided with a cylinder I 8 in which there is operatively disposed a supercharger piston l9 connected by a rod 26 to a steam actuated return piston 2! which is contained in a cylinder 22 located in the upper region of the portion 6. Rigidly secured to the upper side of the piston 2| is an inverted U- V r 9 Claims. (Cl. 230-53) 2 mounted a fluid inlet valve 25 which is arranged to permit inlet fluid to flow through a passage 2-5 to the cylinder l8 and to the cylinder IT.

The low pressure air cylinder I? is ciosed at its lower end by a portion of the upper surface of the cover portion 5. Formed in this portion is an inlet valve chamber 2'! connecting with the chamher at the under side of piston to in cylinder]? by way of a passage 28. In the chamber 2'! there is operably mounted a valve 29 which may open and close communication between the chamber 2'! and the'inlet assage 26 and which is spring biased toward closing position.

The upper end of the low pressure air cylinder i l is closed by the connecting portion 3 in which is formed a similar inlet valve chamber 30 open at all times to the chamber at the upperside of piston it in the cylinder ll by way of passage 3! and open to inlet passage 26 when asimilar spring biased valve 32 mounted in chamber 3ilis unseated in response to inlet air pressure.

In the central part of the portion 3 there is formed a valve chamber 53, which is open to the chamber at the lower side of high pressure air piston H by Way of a passage 34. In this part there is also formed a valve chamber 35 which is open to the chamber at the upper side of piston H by way of a passage 35. Mounted in the chamber 33 are check valves 31 and 38 which have a sprin 39 interposed between and operatively engagin them so as to urge valve 37 upwardly to seat against atmosphere and valve 38 downwardly to seat against the pressure of air above the low pressure air piston it. ,Mounted in the chamber 35 are check valves 49 and Ali which have a spring 42 interposed. between and shaped valve actuating member Zia which is arranged to unseat an exhaust valve 23.

This valve, preferably of the tapered type, may engage a correspondin valve seat formed in the interior surface of the upper end of the cylinder l8 and is Provided with a stem 24 which is slidably guided in a bore in the portion 5. This stem is so located that it will be engaged by the actuating member 2| a when the connected piston is nears the end of its downward stroke as will appear more fully later.

The lower end of the cylinder i8 is closed by a pressure head 4a which is carried by the compressing portion 4. In this head there is operably operatively-engaging them so as to urge valve 48 upwardgy to seat against atmosphere and valve 4| downwardly to seat against the pressure of air under piston E transmitted therefrom by way of a passage 43.

The high pressure air cylinder I2 is closed at the bottom by another part of cover portion 5.-

In this part of the portion 5 there is formed a discharge valve chamber 44 in which is operably mounted a sprin biased valve 45 which, in response to the force of high pressure air, opens communication from the lower end of cylinder 12 to chamber 44. From this chamber air may flow through a passage 46 to an air discharge port 41'.

The cylinder I2 is closed at the top by a part of connectin portion 3 in which is formed a similar discharge valve chamber 48 containing a similar spring biased valve 49 which controls communication between the upper end of cylinder l2 and passage 46 in the same Way as does valve 45 at the lower end.

Mounted in the valve portion 2 is a main valve mechanism, for governing the flow of steam to and from the steam cylinders and the supercharging cylinder, and also mounted in this valve portion is a reversing valve mechanism which controls the movement of the main valve mechanism by controlling the supply of steam thereto.

The supply of steam to these valve mechanisms is in turn controlled by an intercepting valve mechanism which is mounted in the steam portion I, intermediate the low pressure steam cylinder It and the cylinder 22.

The reversing valve mechanism comprises a series of connecting piston heads 58, ill, 52 and 53 which may be reciprocated in a vertical bore 55 by the piston 9 through the medium of a reversing rod 55 in the usual manner.

Thus, there is a chamber 55 defined by the Wall of the bore 55 and piston heads 59 and El, and a chamber 5? defined by the wall of bore il l and piston heads 52 and 53.

The main valve mechanism comprises a series of connected piston heads 58, 59, 66 and Si having the same diameter, and a differential piston head 62 having a larger diameter than the other heads, all of which are reciprocable horizontally in a bore 63 ,as determined by the position of the reversible valve mechanism,

At the left-hand end of the bore 63 there is defined by the walls of the bore and the piston head 58 a chamber-64%. A chamber 55 is defined by the wall of bore $3 and piston heads 58 and 59. A chamber iii; is defined by the wall of bore 53 and piston heads 59 and Gil. A chamber 61 is located between piston heads 69 and iii and a chamber 68 is located between chambers 6i and 62 and at the right-hand face of piston 62 there is a chamber 69.

With the reversing valve mechanism in its uppermost position as shown and with the main valve mechanism in its extreme position to the left as shown, chamber 555 is connected to passage Til which at all times is open to atmosphere. With the reversing valve mechanism in its lowermost position, the piston head 50 closes communication between the chamber 56 and the atmospheric passage l6. Further with the valve mechanism in this latter position, the piston head 5i uncovers passage H thereby connecting the chambers 56 and 69.

Chamber all is always connected to a steam supply passage '52 leading from the intercepting valve mechanism, and as shown may conduct steam to chamber 89 by way of passage 13. In the lower position of the reversing valve mechanism passages i2 and 73 are closed off by piston head 52,

Chamber 6% in the main valve mechanism is always open to steam supply passage l2 and may, as shown, conduct steam to the chamber at the upper side of piston 9 by way of passage hi, which latter passage will be closed off by piston head 61 when the piston assemblage is moved from its left-hand position.

Chamber fi'l is always connected to a passage 15 which leads to the under side of a ball check valve it the upper side of which valve is connected to the intercepting valve mechanism through a passage ll. With the piston Be positioned as shown, chamber 5? is connected to atmosphere by way of passage Illa, but in its other position connects passage 75 to passage i l leading to the chamber at the upper side of piston ii.

With the main valve mechanism positioned as shown, chamber 65 connects a passage 18 leading from the chamber at the under side of piston 9 to a passage 19 leading to the under side of a ball check valve 80, the upper side of which valve is open to the intercepting valve mechanism. With the main valve mechanism in its other position, chamber 66 connects passage 19 to atmospheric passage 76a,

Chamber 65 is always open to steam supply passage '42 and in its right-hand position conducts steam to the chamber at the under side of piston 9 by way of passage l8.

Chamber 6% is closed by piston 58 when the main valve mechanism is in the position in which it is shown, but in its other position is open to atmosphere by way of passage Nib.

The intercepting valve mechanism comprises a multiple head piston member Bl slidably mounted in a bore 82 in the steam portion i, into which bore is pressed a bushing 83 for sliding and port controlling engagement with the stem B l oi the piston member. Directly over the bore 82 there is formed in the valve portion 2 a chamber 85 in which is mounted a spring 56 for determining the movement of the piston member 8i in either direction from the position in which it is shown.

Held in abutting engagement with the upper inner surface of the chamber 85 by the spring til is an annular vertically movable spring seat member 81 which extends through an opening 88 in the top wall of the chamber 85 and through which the upper end of the stem 85 extends. Above the member 8i there is secured to the stem 84 a cross-member 89 which engages the upper surface of the member Sl' so as to transmit the downward movement of the stem to the spring t6.

Held in abutting engagement with the lower inner surface of the chamber 85 is an annular spring seat member 39, the lower surface of which may be engaged by a shoulder 90 formed on the upper end of stem 8% so that the member 8Q may be moved upwardly against the pressure of the spring 8%.

The piston member at comprises integrally connected piston heads at, 82, Q3, 94, and 98. Defined by the lower end surface and wall of the bore 32 and the piston head ill is a chamber 9? which is open to the upper side of the ball check valve 8?) and by way of passage 98 to the chamber at the upper side of piston i3 when it is at the bottom of the low pressure cylinder Hi. This chamber will also communicate by way of passage 99 with the under side of piston !3 instead when piston head 9% crosses the mouth of passage 99 in the upward movement of piston member 8! from the position in which it is shown.

Defined by the wall of bore 82 and piston heads 92 and Q3 is a chamber the which with the piston assemblage in the position illustrated, is in communication with low pressure steam cylinder I i by way of passage lei and with the chamber at the upper side of piston H3 in the supercharging cylinder !8 by way of passage W2.

Defined by the wall of the bore 82 and the piston heads $4 and 95 is a chamber 533 which with the piston assembly positioned as shown is connected to steam supply pipe the through passage iilfi and to the main valve mechanism and reversing valve mechanism by way of passage 12.

Defined by the lower surface of the bushing 83, wall of the bore 82 and the piston head 96 is a chamber the which is open to the upper side of the ball check valve '56 by way of passage ii and may connect, by way of passage lill, with the chamber at the under side of piston 43 when it is at the top of its stroke. This chamber may also communicate with the chamber at the upper side of piston I3 when piston head 96 crosses the mouth of passage I08 in its downward movement from the position in which it is shown.

Leading from the steam supply pipe I M is a restricted passage H39 which conducts steam through the wall of the bushing 83 to the surface of that portion of the stem 84 which is in closely fitting sliding engagement with the bushing 83. This passage also conducts steam to the chamber at the under side of piston 2| for the purpose of returning the supercharging piston I9 to the position shown after it has completed its downward stroke.

The piston stem 84 is provided with a transverse port IIU which will, when the piston member is in its extreme lower position, connect passage I99 with port III, in the bushing 33, and passage 11. With the piston member 3! in its extreme upper position port I I2 in piston stem 84 registers with passage I09 and extends longitudinally through the stem to conduct steam to chamber 91 at the lower end of the piston member.

A ball check valve H3 is operatively mounted in the center portion 3 with its under side open by way of passage H4 to the chamber at the under side of piston I3 and its upper side open to passage I9 so that any steam or air trapped in cylinder !4 during the downward movement of the piston may flow to atmosphere through passage 19 and chamber 61 which at this time will be open to atmosphere by way of passage a.

In a, similar manner ball check valve H5 is operatively mounted in portion 2 to permit trapped air or steam on the upper side of piston I3 to pass to atmosphere by way of passage I5, chamber 61 and passage 'Iila.

Operation With the several parts of the compressor in the position illustrated, the high pressure steam piston 9 has just completed its upward stroke. Near the end of this stroke, the reversing rod 55 was moved upwardly by the piston 9 in the usual manner, thereby moving the reversing valve mechanism into the position illustrated. The connection of main valve chamber 69 to atmosphere by way of passage TI, chamber 56 and passage iii was closed off by piston head 5L Steam passed from pipe I04 through port I65 and chamber I33 in the intercepting valve mechanism to passage I2 from whence it passed directly to chamber 69 and, by way of reversing valve chamber 51 and passage I3, to chamber 63. The combined pressure of steam on the right-hand sides of main valve pistons 58 and 62 caused them to move toward the left-hand end of bore 63 into the position illustrated.

In this position of the main valve mechanism, steam flows from the chamber at the under side of piston 9 in the cylinder 8 through passage 73 to main valve chamber 66. From this chamber the steam flows through passage I9 and past ball check valve 89 into chamber 91 on the under side of piston head 9!, causing intercepting valve piston member BI to move against the pressure of spring 86 into'its upper position.

With piston member 8| in its upper position, chamber 3'! is connected tothe chamber at the ber 91 and passage 99 to actuate low pressure steam piston l3 upwardly.

Also, in this position of member 8|, port H2 registers with passage I09 so that steam may also flow from supply pipe I04 at a restricted rate to chamber 9'! and to the chamber at the under side of piston I3 to insure that the piston will complete its upward stroke.

At the same time, the steam supply passage 12 is closed 011 by piston head 94 and the passage IE2 is closed off by piston head 92, so that neither the high pressure steam piston 9 nor the supercharging piston I9 will operate.

Previous to this action, low pressure air cylinder I! had been supercharged with air under pressure on the upper side of piston I6 by the supercharging piston I9 in a manner to be more fully described later.

,As piston [6 moves upwardly with piston I3, air under pressure is delivered past check valve 38 int chamber 33 and thence by way of passage 34 to the chamber at the under side of the piston II mounted in the high pressure air cylinder I2. Also air is drawn into the chamber at the under side of piston I 6 from atmosphere by way of check valve 25, passage 26, past valve 29, through chamber 21 and passage 28.

When the steam piston I3 reaches the end of its upward stroke, steam in the chamber under the piston will pass into chamber I66 by way of passages I ill and TI and thus substantially equalize the steam pressures in the chambers above piston head 96 and below piston head SI. With the steam pressures thus equalized, spring 83 will return intercepting piston member 8| to the position in which it is shown.

With the intercepting valve mechanism in the position shown and piston I3 at the top of cylinder I4, steam in the chamber under piston l3 will flow through passage lElI, chamber Hill and passage I02 into the chamber at the upper side of under side of low pressure steam piston I3 by way 7 the supercharging piston I9. In response to this pressure, piston I9 will move downwardly forcing the air in the chamber at the underside of the piston through passage 26, past valve 29, through chamber 21 and passage 28 into the chamber beneath the piston I6.

When the piston l9 nears the end of its downward stroke, the actuating member Zla moving with the piston, will engage the stem 24 to unseat the valve 23 and vent the steam from the chamber at the upper side of piston is to atmosphere. With the steam pressure on piston l9 substantially reduced, piston 2|, under the pressure of steam from passage I99, will move upwardly carrying with it the piston rod I9 and thereby piston I9. As piston I9 nears the position in which it is shown it will engage the lower surface of valve 23 and move it to its closed position.

The piston I9 as it was moving upwardly sucked air past check valve 25 and through passage 26 into the chamber beneath the piston in readiness for the next supercharging stroke.

With the valve mechanisms in the positions shown, steam also flows from steam supply pipe I 84, through passage I05, chamber I03 and passage 72 to chamber 68 in the main valve mechanism. From this chamber, steam will flow through passage I4 into the chamber above the piston 9 in the high pressure steam cylinder 8 to cause the steam piston 9 and thereby the high pressure air piston II to move downwardly.

When piston II was being moved, upward by piston 9, air was drawn from atmosphere past check valve 31, through chamber 33 and passage M into cylinder m. When piston it was being moved upward the supercharged air in the chamber at the upper side of the piston was compressed past check valve through chamber and passage 3d into cylinder 52. As piston i i moves downwardly, the air so compressed is now transmitted under high pressure past valve d5, through chamber i land passage til into air discharge port 37 and a suitable reservoir, not shown. At the same time, air is drawn from the atmosphere past check valve to through chamber 35 and passage into the chamber at the upper side of piston ii.

It should be note:- that the supercharging piston and the high pressures steam piston move substantially concurrently since the control of the ports which supply steam to these pistons is so incorporated in the intercepting valve mechanism that the ports are open only in the position illustrated.

As the piston 9 approaches the end 01 its downward stroke, the reversing rod 55 is moved downward by piston in the usual manner, thereby moving the reversing valve mechanism into its lower position. (lhamber 5'3 which formerly conducted steam to the main valve chamber 69 by way of passage 53 is now closed ofi therefrom by piston head Chamber which is constantly open to atmosphere by way of passage lil is now also open to main valve chamber 69, thereby venting the steam pressure from this chamber 69 to atmosphere.

With chamber 3% vented to atmosphere and chamber 68 open to a steam supply from passage 12, steam pressure in this chamber will cause the main valve mechanism to move to its righthand position.

Chamber M will be connected by way of passage i i to the steam chamber at the upper side of the piston 9. It will also be connected by way of passages l5 and ll to chamber its in the inter cepting valve mechanism. Steam will flow from this steam chamber throu h passage chamber and passage iii, past ball check E6, through passage ll and into chamber ass above piston head 95 and move the piston member 8% to its lower position.

Chamber to new connects to the upper side of valve 553 and to passage Eda so that fluid in the chamber at the under of the piston it may pass to atmosphere by way of passages lid and it, chamber Ell and passage Chamber iiil, although connected to passage ii and also to the chamber at the under side of piston 53, cannot transmit steam at this time because the steam supply to passage l! is interrupted as will appear later. Chamber Ed is open to atmosphere by way of passage 3% to eliminate differential pressure opposing move ment to the left for the next stroke.

With piston member 8! in its lower position, steam in chamber r155 will flow by way of passage ltB to the chamber at the upper side of piston 53. Thus steam from the chamber above the high pressure steam piston 9 will be eX- panded into the chamber above low pressure steam piston i3 when the intercepting valve mechanism i in its lower position.

Steam passage will be connected by pas sage lid to passages ill and El to augment the steal supply from the chamber above the pisston d and insure the completion of the downstroke of the piston i3.

Delivery of steam from pipe Hi5 to passage l2 and to the chamber at the under side of the 8. high pressure steam piston 9 will be intercepted by piston head- 95.

The flow of steam from the chamber at the under side of the low pressure steam piston l3 to the chamber above the piston l9 will be interrupted by piston head 93 closing passage I02. Passage as will be blocked between piston heads 35 and s2, so steam and air in the chamber underneath piston is will be permitted to exhaust to atmosphere through passage H4, past ball check valve iill, and through passage 19 and chamber 6-? to passage lila and atmosphere.

When the piston 53 reaches the end of its down-stroke, the chamber at the upper side of he piston is connected to chamber 3'! by way of passage 93. With the pressures above piston head it and below piston head 9| equalized, piston member at will be returned by spring as to t ;e position in which it is shown. Steam will flow from the chamber at the upper side of piston iii to chamber at the upper side of piston I9 to produce the supercharging action previously described when pistons i3 and 553 were at the end of their upstroke. This time however air will flow past check valve 32, through chamber 30 and passage to the chamber at the upper side of piston The main valve piston being now in its righthancl position, steam may flow through chamher it?) in the intercepting valve mechanism, i2, chamber 65, and passage M to the chamber at the under side of piston 9 and cause piston 33 to move upward.

as piston as moves downward it will force compressed air in cylinder ll through passage past valve li into chamber 55, and through passage 35 to the chamber at the upper side of piston ii. As piston ll subsequently moves upward it will deliver this air past check valve 45, through chamber and passage db into the discharge pipe M and an air reservoir, not shown.

Summary The intercepting valve mechanism in normal position as shown, passes live steam to the high pressure steam piston 9 for its next stroke and also passes exhaust steam from the low pressure cylinder is to the supercharging cylinder l8. In its upper position it intercepts this flow of steam to the piston 9 and from the low pressure cylinde it and passes steam from the under side of n pressure steam piston 9 to the under side he low pressure steam piston l3. in its lower position it intercepts the flow of steam to the piston 9 and from the low pressure cylinder l8 and passes steam from the upper side of piston S to the upper side of piston IS.

The reversing valve piston member moves upwar 13 when piston s completes its up-stroke car ing the main valve piston member to move to the left. The intercepting valve piston memlsi is then moved upwardly by steam from under side of piston S, which steam is then delivered to the under side of piston it to move it upwardly. At the top of the stroke of piston is the intercepting valve mechanism returns to s normal position.

When the low pressure air piston 55 moves upwardl with piston 53, the air under pressure in the chamber above piston it is transferred to the underside of the high pressure air piston H which is at the top of cylinder i2 and air is drawn from atmosphere to the under side of piston i6;

Whil piston it remains at the top of cylinder H, the supercharging piston it charges the chamber at the under side of piston 16 with air. under pressure. At the same time the high pressure air piston l moves downwardly transferring the air under pressure in the chamber at the under side of piston H to a suitable reservoir. As this piston moves down air is drawn from atmosphere to the chamber at the upper side of it.

The reversing valve piston member moves downwardly when piston 9 completes its down-stroke causing the main valve mechanism to move to the right. Piston member 8| is then moved downwardly by steam from the chamber at the upper side of piston 9, which steam is then-delivered to the chamber at the upper side of piston l8 to move it down. At the bottom of the stroke by piston l3, piston member 8| returns to its normal position.

In normal position of piston member 8| the supercharging piston I9 is again actuated and at the same time high pressure steam piston 9 is again actuated upwardly.

When the low pressure air piston It moves down with piston l3, the'supercharged air in the chamber at the under side of piston I6 is transferred to the chamber at the upper side of piston II which is now at. the bottom of cylinder l2. Air is drawn from atmosphere to the chamher at the upper side of piston l6.

While piston l6 remains at the bottom of cylinder H, the supercharging piston l9 charges the chamber at the upper side of piston l6 with air under pressure. At the same time the high pressure piston H moves'upwardly, transferring the air under pressure from the chamber above piston H to a suitable reservoir. As this piston moves upwardly air is drawn from atmosphere to the chamber at the under side of it.

Having now described my invention, what I claim as new and desire to secure by Letters Patent is:

1. A steam driven air compressor, in combination, a first steam operated piston and cylinder means for compressing air into a reservoir, a second steam operated piston and cylinder means for compressing air into said first means, a third steam operated piston and cylinder means for compressing air into said second means, and valve means conditionable upon the position of the piston of said first means to control the sequence of operation of the three said means,

said valve means being effective in one position to admit steam to said first means and to said third means and being efiective in another position to interrupt the steam supply to said first means and to said third means and to supply steam to said second means.

2. A compound steam driven air compressor, in combination, a high pressure air compression cylinder and piston, a high pressure steam engine cylinder and piston for operating said air compression piston, a low pressure air compression cylinder and piston, a low pressure steam engine cylinder and piston foroperating said low pressure air compression piston, a main valve mechanism operative for supplying steam to said high pressure steam cylinder and exhausting steam therefrom to said low pressure steam cylinder, a reversing valve mechanism actuated by the high'pressure steamrpiston for controlling the operation of said main valve mechanism, an intercepting valve mechanism operative in response to the pressure of exhaust steam from said high pressure steam engine for so controlling the supply of steam to said high pressure steam cylinder and to said low pressure steam cylinder that one engine is rendered inoperative while the other operates, valve means for admitting air from the atmosphere to said low pressure air cylinder before the beginning of the stroke of the low pressure air piston, and valve means for admitting air from the atmosphere to said high pressure air cylinder before the beginning of the stroke of the high pressure air piston.

3. A compound steam driven air compressor, in combination, a high pressure engine cylinder and piston, a low pressure engine cylinder and piston, a high pressure air compressing cylinder operatively related to said first eng a 10W p sure air compressing cylinder operatively related to said second engine, a main valve mechanism governing the supply of steam to said high pressure engine and the transfer of exhaust steam therefrom to said low pressure engine, a reversing valve mechanism actuated by said high pressure engine piston for controlling said main valve mechanism, intercepting valve means controlled by said main valve mechanism for so controlling the supply of steam to said high pressure engine and said low pressure engine that one engine is maintained inoperative While the other engine.

operates, means responsive to the pressure of exhaust steam from said low pressure engine to supercharge said low pressure air cylinder, and means controlled by said low pressure engine for transferring exhaust steam therefrom to said supercharging means when said low pressure engine is inoperative.

4. A compound steam driven air compressor, in combination, a high pressure air compression cylinder and piston, a high pressure steam engine cylinder and piston for actuating said air piston, a low pressure air compression cylinder and piston, a low pressure steam engine cylinder and piston for actuating said low pressure air piston, steam operated means for supercharging said low pressure air cylinder, valve means conditionable upon the position of the high pressure steam piston to control the sequence of operation of said steam engines and said supercharging means, said valve means being operative in one position to admit live steam to said high pressure steam cylinder and to transfer exhaust steam from said low pressure steam cylinder to said supercharging means and operative in another position to interrupt the flow of steam to said high pressure steam cylinder and to said supercharging means and to transfer exhaust steam from said high pressure steam cylinder to said low pressure steam cylinder.

5. A compound steam driven air compressor, in combination, a high pressure air compression cylinder and piston, a high pressure steam engine for actuating said air piston, a low pressure air compression cylinder and piston, a low pressure steam engine for actuating said low pressure air piston, means responsive to exhaust steam from said low pressure engine for supercharging said low pressure air cylinder, a valve mechanism controlled by the piston of said high pressure steam engine for controlling the supply of live steam thereto and the exhaust of steam therefrom to said low pressure steam engine, intercepting valve means rendered efiective when said low pressure steam engine completes its stroke to suspend the operation thereof while said high pressure steam engine and said supercharging means operate and rendered effective when said high pressure steam engine completes its stroke to suspend the operation thereof and of said supercharging' means while said low pressure steam engine opcrates.

6. A compound steam driven air compressor, in combination, a first steam operated piston and cylinder means for compressing air into a reservoir, a second steam operated piston and cylinder means for compressing air into said second means, a third steam operated piston and cylinder means for compressing air into said second means, valve means controlled in accordance with the operation of the piston of the-first said means to control the operation of all of said steam operated piston and cylinder means, said valve means being operative in one position to deliver steam to said first means and to transfer steam from said second means to said third means and operative in another position to interrupt the delivery of steam to said first means and the transfer of steam from said second means to said third means and to transfer steam from said first means to said second means, and means rendered effective by the piston of said second means, to return said valve means to its first mentioned piston. V

7. A compound steam driven air compressor comprising a high pressure air compression cyl inder and piston, a high pressure steam cylinder and piston for actuating said high pressure air piston, a low pressure aircompression cylinder and piston,a low pressure steam cylinder and piston for actuating said low pressure air piston, a main valve mechanism operative in accordance with the operation of the hi h pressure steam piston for controlling the supply of live steam to the high pressure steam cylinder and the exhaust of steam therefrom to the low pressure steam cylinder, a cylinder and piston means responsive to the pressure of exhaust steam from the low pressure steam cylinder to supercharge the low pressure air cylinder, an intercepting valve mechanism having a position to which it is moved in response to the pressure of exhaust steam from the high pressure steam cylinder when the high pressure steam piston is at substantially the end of its stroke in which position said mechanism effects-the suspension of the operation of the high pressure steam piston and of said supercharging piston and permits the low pressure steam piston to make its stroke, and means operative when the low pressure steam piston has completed its stroke to move said intercepting valve mechanism to another position in which the mechanism suspends the operation of the low pressure steam piston while permitting the high pressure steam piston and said supercharging pistons to complete their strokes.

8. A multiple stage air compressor comprising a first cylinder and piston means for compressing air into a, reservoir while charging its non-pressure side with air from the atmosphere, a second cylinder and piston means for compressing air into the first means while charging its nonpressure side with'air from, the atmosphere, a first engine responsive to the pressure of live steam to actuate said first means, a second engine responsive to the pressure of exhaust steam from said first engine to actuate said second means, a third cylinder and piston means chargeable with air from the atmosphere upon movement of the piston thereof in one direction and operative in the opposite direction in response to the pressure of exhaust steam from said second engine to compress air with which it has been charged into said second means, a third engine responsive to the pressure of live steam to cause the piston of said third means to make its charging stroke, a main valve mechanism for controlling the admission of steam to and the exhaust of steam from said first and said second engine, a reversing valve mechanism actuated by said first engine for controlling the operation of said main valve mechanism, an intercepting valve mechanism effective in one position to admit live steam to said main valve mechanism, thereby causing said first engine to operate, and to admit exhaust steam from said second engine to said third means to cause the third means to compress air, said intercepting valve mechanism being responsive to the pressure of exhaust steam from said first engine to move to another position and being efiective in said other position to admit the exhaust steam from said first engine to said second engine to render the latter operative, and being further efiective to interrupt the flow of live steam to said first engine and the flow of exhaust steam to said third means to thereby render them inoperative, and means for returning said intercepting valve mechanism to the first position when said second engine has substantially completed a stroke. 9. A compound steam driven air compressor, in combination, a first steam operated piston and cylinder means for compressing air into a reservoir, a second steam operated piston and cylinder means for compressing air into said first means, a third steam operated piston and cylinder means for compressing air into said second means, a reversing valve mechanism positioned by the piston of said first means to supply steam to one side or the other of the piston of said first means and to transfer steam from said first means to one side or the other of the piston of said second means, intercepting valve means controlled in accordance with the operation of the piston of said first means to move to one or the other of two positions to interrupt the supply of steam to said first means and the transfer of exhaust steam from said second means to said third means and to transfer the exhaust steam from said first means to said second means, said intercepting valve means being movable to a third position in accordance with the operation of the piston of said second'means, to interrupt the transfer of exhaust steam from said first means to said second means and to supply steam to said first means and to transfer exhaust steam from said second means to said third means.

BURTON S. AIKMAN.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 412,474 Cummings Oct. 8, 1889 521,432 Chaplin June 12, 1894 626,652 Dean June 6, 1899 723,001 Marsh Mar. 17, 1903 1,039,616 Tuma Sept. 24, 1912 2,143,179 Baker Jan. 10, 1939 

